Alkali metal alumino silicates,methods for their production and compositions thereof

ABSTRACT

THE SUBJECT MATTER OF THE FOLLOWING SPECIFICATION CONCERNS THE PRODUCTION OF FINELY DIVIDED MATERIALS USEFUL AS PIGMENTS, MOOSTURE CONDITIONERS, PAPER FILLERS, AND IN RUBBER REINFORCEMENT AND THE LIKE. CONSIDERING PRESENT ECONOMICS, PERHAPS THE MOST PRACTICAL EMBODIMENT OF THE SUBJECT MATTER EMPLOYS THE REACTION OF A SOLUBLE SODIUM SILIDATE AND ALUMINUM SULFATE IN PRODUCING PRECIPITATES COMMONLY KNOWN AND IDENTIFIABLE AS SODIUM ALUMINO SILICATE, THE PRECIPITATE BEING ULTIMATELY COLLECTED AS A DRIED PARTICULATE MATERIAL OF SUB-MICRON PARTICLE SIZE. THE DISCLOSED PROCESS INVOLVES CONDUCTING THIS GENERAL TYPE OF REACTION IN THE PRESENCE OF CALCULATED QUANTITY OF SODIUM SULFATE FROM THE OUTSET OF THE REACTION WHEREBY ECONOMICS ARE IMPROVED AND HIGHLY REFINED MODIFICATIONS IN THE CHARACTERISTIC OF THE FINAL MATERIALS BECOME OBTAINABLE. THE REACTION MAY BE VARIED ACCORDING TO SEVERAL CONDITIONS, SUCH AS PH, TEMPERATURE, CONCENTRATION, MANNER OF FEEDING MATERIALS AND THE LIKE WHEREBY TO BETTER ADAPT THE NEW MATERIALS TO HIGHLY SPECIALIZED NEEDS, SUCH AS IN RUBBER COMPOUNDING AND PAPER PRODUCTION.

United States Patent Oflice 3,832,327 Patented Aug. 27, 1974 ALKALIMETAL ALUMINO SILICATES, METHODS FOR THEIR PRODUCTION AND COMPOSITIONSTHEREOF Lowell E. Hackbarth, Bel Air, Md., and Joseph T.

Crockett, Auburn, Ala., assignors to J. M. Huber Corporation, Borger,Tex.

No Drawing. Application Feb. 3, 1971, Ser. No. 112,469,

now Patent No. 3,746,559, which is a continuation-inpart of applicationSer. No. 730,892, May 21, 1968, now Patent No. 3,582,379. Divided andthis application July 20, 1972, Ser. No. 273,674

Int. Cl. C08c 11/12 US. Cl. 26042.37 1 Claim ABSTRACT OF THE DISCLOSUREThe subject matter of the following Specification concerns theproduction of finely divided materials useful as pigments, moistureconditioners, paper fillers, and in rubber reinforcement and the like.Considering present economics, perhaps the most practical embodiment ofthe subject matter employs the reaction of a soluble sodium silicate andaluminum sulfate in producing precipitates commonly known andidentifiable as sodium alumino silicates, the precipitate beingultimately collected as a dried particulate material of sub-micronparticle size. The disclosed process involves conducting this generaltype of reaction in the presence of calculated quantity of sodiumsulfate from the outset of the reaction whereby economics are improvedand highly refined modifications in the characteristic of the finalmaterials become obtainable. The reaction may be varied according toseveral conditions, such as pH, temperature, concentration, manner offeeding materials and the like whereby to better adapt the new materialsto highly specialized needs, such as in rubber compounding and paperproduction.

This is a division of application Ser. No. 112,469, filed Feb. 3, 1971,now US. Pat. 3,746,559, which is a continuaion-in-part of applicationSer. No. 730,892, filed May 21, 1968, now US. Pat. 3,582,379.

BACKGROUND OF THE INVENTION This invention relates to the production offinely divided materials having a variety of uses such as pigments,moisture conditions, etc., but which are especially useful as rubberreinforcing materials and in paper making. The pigments of the inventionare produced by the reaction of a water soluble alkali metal silicatewith water soluble aluminum salts of strong acids, preferably by thereaction of sodium silicates and aluminum sulfate, according to methodsgenerally related to those described in US. Pat. No. 2,739,073. Theproducts resulting from the process of this patent, as well as from thesimilar process of this invention, are, in the sodium form, sometimesdescribed as sodium silico aluminates, sodium alumino silicates,synthetic zeolites, mineral pigments and the like.

SUMMARY OF THE INVENTION Although the products of the present processare in general much the same in chemical content as those described inthe aforementioned patent, they are markedly different in their physicalnature and surface chemistry.

In particular, it is concluded that they differ as regards to theirparticle size, the chemical nature of the particle surfaces, and in thenature of the state of aggregation, which characteristics are regardedas of primary interest in the rubber reinforcing class of syntheticsilicas and silicates. While the products obtainable according to theaforesaid patent have good utility in rubber compounding and papermaking, the markedly different products of this invention are found tobe quite superior, at least insofar as at present has been demonstratedin actual practice. More specifically, the new products of the presentinvention are at least comparable in utility to the present best knownrubber filler materials, while also having other valuable improvedutility in paper production. Therefore, the new products herein, may bereadily distinguished from those of the said patent on the basis ofrubber suitability criteria alone, and perhaps better so on such basissince certain highly technical physical properties by which they may bedistinguished are at least to some extent speculative. Moreover, theprocess involved herein is significantly different.

In addition to their improved qualities, the new products are producibleat considerable economic advantages over prior similar materials.

As regards to the economic advantages, such are illustrated in relationto the type of products resulting from the process described in US. Pat.No. 2,848,346, which products are currently accepted as being highlysuitable for rubber compounding. In fact these latter patented productspossess the very optimum properties according to current standards. Aswill be observed upon reference to this patent, products are producedwhich are referred to as hydrated silicas (pigments are hydrated) andsuch hydrated silicas are produced by a different method, namely, byreaction of dilute sodium silicates with dilute sulfuric acid. Althoughthe products of this latter patent are presently more suitable thanthose of the aforesaid Pat. No. 2,739,073 as regards to rubbercompounding in particular, various factors involved in their production,including raw material costs, lead to higher product costs. The presentinvention provides end products which are at least equal in valuableproperties to those of the latter patent while being obtainableaccording to the general and less costly process of the former patent.

A further improvement in the process of this invention arises inconnection with the economics of sodium sulfate recovery, this saltbeing a by-product of the reaction. More specifically, the presentprocess involves the deliberate addition of sodium sulfate as a part ofthe reaction medium, as a result of which the sulfate wash liquorcontains a much higher concentration of sodium sulfate, i.e., thequantity added plus the amount normally produced in the reaction. Sincethe quantity of Water used for washing the reaction products free ofsodium sulfate is the same whether sodium sulfate is added or not, theresult is that the wash liquor contains a much higher concentration ofthis salt and is therefore more economical to recover. As will be seenhowever, the addition of sodium sulfate has significance other than thisadvantage.

Another advantage of the invention which flows directly from reactingthe materials from the inception of the reaction in the presence ofsodium sulfate is that the resulting product is more uniform throughouta particular batch. It appears that sodium sulfate has a pronouncedeffect upon the nature and size of the aggregate, the tendency beingtoward the formation of smaller aggregates, together with an increase insurface area and oil absorption properties. It is thought possible thatthis advantage is due basically to the more uniform chemical reactionconditions of the present process in contrast to prior processes. Thebasic reaction heretofore known products sodium sulfate. As the reactionproceeds over a period of time, sodium sulfate, starting from zeroquantity, builds up to the total amount formed at the conclusion of thereaction. As will be recognized, therefore, the reaction environment isquite different at the beginning as compared with the environment afterseveral minutes, and it constantly changes until complete. By providinga substantial amount of sodium sulfate from the beginning, the effectsof this salt are present from the beginning so that a period of timedoes not exist when the effects are com pletely absent and there is noperiod of time when there is less than the optimum amount of the salt.The optimum amount, as well as useful minimum amounts, are acontribution of this invention.

Prior to this invention, it was not thought that the reaction of sodiumsilicates with aluminum sulfate could be conducted in such a manner asto effect a truly significant change or changes in the nature of the endproducts, at least as regards to those characteristics important in theart of rubber reinforcing. Thus, the present invention, whichdemonstrates clearly to the contrary, involves a highly revealingdiscovery in the art of silica-type pigment production. As is becomingmore and more apparent, the chemistry and the chemical nature of thesurface of the synthetic silicas and silicates is very complex indeed,and it appears that a considerable amount of additional insight remainsto be gained concerning them before they can be considered to besubstantially totally understood and evaluated. In the present instance,it is thought to be highly probable that the products obtained aretechnically rather differently structured chemicals from any heretoforeknown; yet demonstration of such fact, followed by the provision of aprecisely distinguishing definition, is at least very difficult withpresent day equipment.

As pointed out above, the products of this invention are similar tothose heretofore produced following the proce dures described in US.Pat. No. 2,739,073. In general, these products are compositionsessentially consisting of alkali metal, aluminum and silicon oxides,obtained in extremely small particle sizes, as very fine precipitates,by suitable commingling and reacting together, at very lowconcentrations, dilute aqueous solutions of an alkali metal silicate anda water soluble aluminum salt such as aluminum sulfate, aluminumchloride, aluminum nitrate or ammonium alum. The precipitated pigmentparticles are substantially all less than one micron in diameter, andthey average less than one-half micron in diameter. In the main theparticles range from about 0.02-05 micron. Moreover, they arecharacterized by extraordinary brightness and by other qualities ashereinafter described which make them exceptionally valuable for uses ofthe nature indicated above.

One of the most important aspects of the present invention involves thediscovery that the basic reaction may be selectively directed to producespecialized forms of sodium silico aluminates. By specialized forms ismeant that the present invention permits one to tailor the end productaccording to the most desirable form 'for use in a particularenvironment. Thus, where a reinforcing material for use in rubber shoesoles, heels, and the like of the highest quality is desired, certainoverall conditions are found to respond to provide an optimum set ofperformance characteristics. The present invention provides suchproducts of highly improved character. Moreover, as is Well known, therubber industry not only requires reinforcing materials having veryparticular performance characteristics, but also the economic aspects ofthe final rubber producing process must not be acected adversely by thematerials added. For example, one may be able to produce a pigmenthaving desired, very fine performance characteristics, but the overallcure time in the rubber process necessitated by such pigment may belonger than a similar pigment having somewhat less acceptableperformance characteristics. This heretofore to some extent has led tothe compromising of quality of the rubber product in view of theimportant economic time factor in the production process. The overallcure time is also of importance in other rubber applications, such as intire production. Accordingly, it is quite important to consider therubber reinforcing art with the entire requirements in mind.

The aspect of the present invention having to do more particularly withrubber reinforcement in the field of tires, involves severalcharacteristics similar to those required in the shoe field; but certainperformance characteristics are required in tires which differsignificantly. In other words, the most desirable tire pigment is notnecessarily equally suitable in the shoe art. The present inventionprovides reinforcing material for tires which are tailored to fulfillspecific needs and which are superior in performance.

Further, where the pigments are to be employed as fillers inpapermaking, certain somewhat different characteristics are desirable.Although any of the pigments produced according to this invention may beemployed as paper fillers with advantages over previous fillers, thosethat are produced under certain controlled conditions are moreespecially desirable because of greater improvement in strike-throughperformance. This is especially important in low grade paper stock, suchas newsprint.

Still further, the pigments produced according to this invention may beemployed in fine paper as paper fillers with certain advantages overprevious fillers, some of which are imparting to fine paper a brightnessthat is at least 0.7 points higher and an opacity that is at least 0.5points higher than the brightness and opacity values imparted by thesodium alumino silicate produced according to methods generallydescribed in US. Pat. No. 2,739,073.

As indicated above, it is not believed that heretofore it has beenpossible to control the basic reaction in a consistent way such as toeffect these relatively delicate modifications of the end productscorresponding to improvements for particular uses.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Although the process of thisinvention involves a number of conditions which are varied according toparticular needs, it has been discovered that a predetermined minimumquantity of sodium sulfate must be present as a part of the reactionmedium from the inception of the reaction; otherwise, the end productsfail to acquire the physical and surface chemical characteristicsfalling within the range of pigments which are considered to be ofimproved nature herein, i.e., an improvement in at least one attribute.(At this point, it may be well to remark that if the general type ofreaction is conducted with a different aluminum salt, for example,aluminum chloride, then the corresponding acid salt is required, that isto say, with aluminum chloride one should employ sodium chloride in thereaction.) Continuing, although the sodium sulfate must be present fromthe beginning of the reaction in a minimum amount, it may be present inquite a large quantity without deleterious effects, at least insofar asthe objects of this invention are concerned. The present inventionteaches a range of sodium sulfate conditions which produces worthwhileresults. It is recognized that if sodium sulfate is present in anunnecessarily large quantity, a reversionary condition sets in and theadvantages otherwise produced according to this invention tend to becomelost. The exact point of this occurrence is exceedingly difficult todefine; and insofar as the point is established quantitatively in thisinvention, it should be understood that it is established in relation tothe performance qualities presently required in the various use areas,and not that a different quantity may produce im proved productsconforming to a changed standard. As those required performancecharacteristics may alter in the future, it is foreseen that a greateror an even lesser quantity of sodium sulfate may be tolerable. It is,therefore, desired to emphasize that the discovery of advantageousresponsiveness of the basic reaction to sodium sulfate in relation to acommunity of products is an extremely important, if not the mostimportant aspect of the present invention. If the sodium sulfateconditions as taught herein are observed in conducting the reaction, animproved product results in at least one important respect which iscommon to the needs of the rubber industry in the overall and at thesame time the pigment has general utility as heretofore known andimproved utility in paper making; moreover, the economics of sodiumsulfate recovery are afforded.

The aspects of the process within the broad inventive concept as abovedescribed which are desirable to be managed for the purpose of producingstill other improved characteristics of the end products in relation tospecial needs are several in number. For example, in order to produce apigment having properties more suitable for the shoe industry, it isgenerally more advantageous to perform the reaction by delivering adilute stream of aluminum sulfate to a pre-established highly dilutesoduim silicate-sodium sulfate solution. Thus, the entirety of thesodium silicate and sodium sulfate calculated to be desirablequantity-wise in relation to the aluminum sulfate constitutes a reactionmedium to which the aluminum sulfate is fed over a given period of time.As will be more fully described hereinafter, the rate of feed of thealuminum sulfate provides a further means of control upon the nature ofthe end product. Still further as regards products having specialutility in the shoe industry, such products may be obtained by varyingthe approach to the reaction somewhat from that which has just beendescribed. More particularly, it is found that the reaction may beconducted with the view to obtaining such improved products varying onlyslightly in character by establishing a sodium silicate-sodium sulfatereaction medium composed of as little as approximately 50% of the totalof such materials calculated to be necessary in the reaction in relationto the aluminum sulfate, the remainder of the sodium silicate-sodiumsulfate solution being fed to the reaction mass as a stream (or streams)concurrently with a separate stream of aluminum sulfate. Here again,some variation of the rate of feed of alumnium sulfate and other processmodifications are possible within limits without destruction ofdesirable qualities of the end product. For example, by feeding a streamof water soluble aluminum salt, more particularly aluminum sulfate, tothe reaction medium of at least ten seconds or more in time in excess ofthe ordinary time generally included within the normal procedure foradding aluminum sulfate to the reaction prior to adding the otherreactant, sodium silicate described in US. Pat. No. 2,739,073 and inco-pending application No. 730,892 filed May 21, 1968, the resultingproduct consequently imparts to fine paper improvements in sheetbrightness and opacity. Modification of the conditions just described,i.e., manner of commingling the reactants, leads to the production ofslightly different products; however, all of the products are improvedin one respect or another over those previously known for use in thesame environment.

Considering the process from a different standpoint, namely, thestandpoint of producing end products having qualities which areespecially desirable in the paper industry and tire field, preferablythe reaction is conducted in a slightly different manner since thedesired differences in the products are significant and demonstrable inuse. In this connecton, and in contrast to the foregoing approach, it isdesirable that the major portions of the reacting materials be fedconcurrently as separate streams to a highly dilute sodiumsilicate-sodium sulfate reaction medium. More especially, a relativelysmaller portion of the pre-calculated amounts of sodium silicate andsodium sulfate (usually herein fed as a single combined stream) isemployed as the reaction medium, the remainder of such pre-calculatedamount constituting the sodium silicate-sodium sulfate feedstream, whichis fed simultaneously with a stream of aluminum sulfate. The propertiesthat are produced according to this technique are found to appearincreasingly prominently in relation to the smallness of the quantity ofsodium silicate-sodium sulfate in the solution which provides thereaction medium. The critical point is in relation to the minimumquantity of sodium sulfate which is desirable to be present initially asa part of the reaction medium. Depending upon the concentration ofsoduim sulfate in the precalculated feedstream, the exact amountdelivered to form the reaction medium will vary. However, for example,in performing the reaction within the preferred conditions herein,approximately 10% of the total quantity of silicate and sodium sulfateare employed to constitute the reaction medium to which the remainder ofthe reactants are delivered over a period of time; and, while stillobtaining a product of improved quality for the particular use, as muchas approximately of the total sodium silicatesodium sulfatepre-calculated amount may be delivered to form the reaction medium.

Thus, it will be observed that the characteristics of the reactionmedium as regards to the quantity of sodium silicate-sodium sulfatecontent therein in relation to the remainder of the reactants to be fedis a significant variable in the tailoring of specific end products.

As a general proposition, once having determined the quantity of sodiumsulfate necessary in the production of a given quantity of end products,regardless of the character of the end prOducts specifically sought, thepresence of more or less quantity of the total sodium sulfate in theinitial reaction batch is not found to be highly critical; but theminimum quantity of sodium sulfate is always provided at the outset ofthe reaction. Thus, the sodium sulfate-sodium silicate does notnecessarily require to be admixed and fed in as a single stream toprovide the reaction medium. Instead, the quantity of sodium sulfate maybe fed separately as a stream; or the total; or any part of the totalquantity thereof, may be pre-delivered to the water mass in advance ofdelivery of the reacting chemicals. Moreover, if desired, the sodiumsulfate may be fed to the reaction medium with the aluminum sulfate, aminimum quantity of the sodium sulfate having been pre-delivered to thereaction zone.

A further significant aspect of the process concerns the pH of the finalpigment end products. In this connection, pigments which are produced byconducting the process within the range of opera ing techniques abovedescribed, and which have improved properties over those heretoforeknown, have a pH value of from about 7 to 11. Moreover, it has beendiscovered as a further aspect of definite relation to the suitabilityof the pigments for the invention that, within this range, pigment pHhas a use in the several different environments generally discussedabove. More particularly, it has been discove ed that when a pigment isproduced having a pH within the range of about 7.2 to 8.5, moreespecially and preferably, within the range of about 7.5 to 8, suchpigments exhibit certain characteristics or properties rendering themmore useful in paper and in the production of rubber tires. Pigmentshaving a pH within the range of about 7 to 8 are found to exhibitcertain characteristics or properties rendering them of improvedusefulness in the shoe industry in the production of soles, heels andthe like. Therefore, looking to the object of providing the tailormadeproducts of the present invention, it is an aspect of the invention tocontrol the pH of the ultimate product.

pH control involves particular adjustment to the initial reactionleading to pigment precipitation. Basically, the reaction is conductedsuch that the final pigment slurry resulting from the reaction fallswithin particular levels according to the desired ultimate pH of thepigment. In the case of products especially useful in paper and also inreinforcing tire rubber, the reaction is controlled to provide a finalslurry pH falling between about 5.5 to 9.5, more particularly andpreferably a pH of about 8 to 7.0. In the casse of pigment productionfor special utility in the shoe industry, the final slurry may fallwithin the same pH range, that is to say about 5.5 to 9.5, however, moreparticularly and preferably, the final slurry pH is controlled such thatits pH is about 5.8 to 6.0. As will be understood by those skilled inthe art, the final slurry pH is directly related to the sulfate ioncontent of the slurry and this is readily controlled by adjustment ofthe quantity of aluminum sulfate which is fed to the reaction. That isto say, since the pH of the final slurry is desired to fall on the acidside, then slightly more aluminum sulfate than needed is provided forreaction with the sodium silicate. Similarly, if a lower slurry pH isdesired, a slightly higher quantity of aluminum sulfate is provided. Itmay be remanked that the higher pH pigments are seen to afford slightlyshorter scorch times in the rubber compounding process. On the otherhand, as the pigment pH increases towards a higher value, the stiffnessquality of the rubber end product begins to degrade slightly.

As will be seen from the foregoing, the desired pigment product pH levelis very readily controlled or established by adjusting the reactionmedium to the acid side with a slight excess of aluminum sulfate. It isnow desired to discuss the matter of pH from another standpoint alsohaving a bearing on the nature of the end products. This additionalstandpoint has to do with the pH of the reaction medium over the periodof time during which the precipitation reaction is taking place. Thisperiod of time may be varied widely; however, in general, the reactionsextend from approximately 20 to approximately 40 minutes for completion,aside from ageing time before the slurry is filtered. Thus, indiscussing precipitation pH, it will be understood that such is inrelation to conditions occurring in such periods of time as well asother times which may be adopted for carrying out the precipitationreaction. As aforesaid, it is found that the precipitation pH levelexerts a marked effect upon the nature of the particles which make upthe final pigment end products. In the case of paper and tire pigments,it is found to be desirable to maintain precipitating pH from about 10.4to 10.9. In the case of products specialized for use in the shoeindustry, it has been found to be desirable to maintain a slightlyhigher pH, that is fro-m about 10.9 to about 11.3, preferably about11.2. It should be pointed out that precise pH values are diflicult toobserve and maintain as a matter of certainty in a given reactionbecause the permissible deviation from the preferred pre- 7 cipitatingpH values is within the limits of error of pH measuring instruments.Therefore, in the present process the reaction conditions are maintainedon the basis of pre-established feed rates of the aluminum sulfate. Aswould be understood, the higher the feed rate for aluminum sulfate, thelower the precipitation pH and vice versa. Of course, where all or amajor quantity of the sodium silicate is present in the reaction mediumfrom the outset of the reaction, alum feed rate has very little effecton pH until that quantity is used up in the reaction.

It is perhaps impossible to offer an unequivocal statement concerningthe physical or chemical modification which is brought about in theprecipitated particles as a result of pH control during theprecipitation reaction or as the pH of the ultimate pigment particles isdifferent. However, insofar as observations are believed to permit, itappears that precipitation pH values as indicated, especially thepreferred levels, lead to the production of more uniform pigmentparticles as regards to their size distribution, which uniformityappears to result by way of reduction of the number of coarser particlesin the mass. It appears that as the precipitation pH is lower there isproduced a larger number of relatively large agglomerated type ofpigment particles. Where the precipitation pH is higher, that is withinthe range preferred herein, the agglomerate structures are smaller;moreover, such pigments are found to have a higher surface area and theagglomerate is less dense.

As regards to the pH of the pigment particle, it is found that higher pHpigments tend to impart a relatively high level of stiffness to therubber products; and, whereas the opposite is true in pigments of lowerpH, the tear resistance of the rubber product is improved. Theseoccurrences are thought to be related to surface chemistrycharacteristics of the particles, considering such in relation toreactions occurring between the rubber and such pigment surfaces.Further discussion on this point at least at this time, is believed tobe entirely theoretical. It is the end result that is accomplished bypigments of the characteristics described herein which are important tonote in examining the matter from the standpoint of improved usefulness,the explanation as to why being in any event unnecessary.

As is well known, the general reaction involving sodium silicate andaluminum sulfate may be carried out over a wide temperature range. Thepresence of the minimum quantity of sodium sulfate throughout thereaction according to this invention requires no particular changes inestablished temperature conditions. According to this in vention, theimproved characteristics of the pigments, which affect their increasedutility in the rubber compounding processes wherein the scorch time ismarkedly reduced, result where the reaction as heretofore described isconducted at a temperature within the range of about 70 F. to about 180F. or higher, although there is no particular advantage in higherreaction temperatures. All things considered in rendering the reactionmore practical, a more suitable temperature range is from about F. toabout 165 F. Preferably, depending upon exactly how the process isconducted, the volume and temperature of reaction medium initiallyestablished, whether it contain all of the sodium silicate-sodiumsulfate solution or only a portion thereof, the aluminum sulfate andsodium silicate streams are adjusted to provide a reaction temperaturefalling within the range of about to about 150, preferably about to Inall cases, however, it has been found to be advantageous to feed thealuminum sulfate stream to the reaction at a temperature as high as thisrange and preferably at a temperature of at least 130 up to about F.depending upon the objective. The importance of the aluminum sulfatetemperature control is thought to be related to modifications occurringin the surface chemistry of the particles of pigments produced.Specifically, certain of the properties of the pigments of the presentinvention are thought to occur according to the coordination of aluminumwith silica, precipitation of the pigment during the reaction beingachieved via aluminum sulfate. It is thought that such precipitation andcoordination depend significantly upon the uniform availability ofaluminum ions in an acidic media. Such availability itself is related tothe dissociation and acidity of the aluminum sulfate, which istemperature related. It may be, therefore, that the recommendedtemperature control of the aluminum sulfate feed stream leads to theproduction of pigments having a higher uniformity of surface chemistrycharacteristic, the reaction environment being such as to affordespecially uniform precipitating and surface coordinating conditions. Itwill be appreciated that such observations may or may not be completelydescriptive of circumstances, at least not entirely so, for the reasonthat a variety of other reaction conditions and relationships areinvolved. Moreover, the matter of surface chemistry must be regarded asat least somewhat speculative at this stage of knowledge of the art, andespecially so where the ultimate properties of the products hereinproduced are attributed to such phenomena.

Where the objective is to produce pigments intended for application inthe shoe industry, as in rubber soles, heels, etc., it has been found tobe more suitable and preferable to feed aluminum sulfate at atemperature nearer the upper end of this temperature range, moreparticularly, about 160 F. The lower end of the temperature range, i.e.,about 130 F. to about 140 F., has been found to be preferable inproducing tire pigments and paper fillers. Insofar as sodium silicatefeed temperature is concerned, this is not critical and it may bedelivered at room temperature up to the desired reaction temperature.

In practicing the invention, a sodium silicate-sodium sulfate solutionis prepared containing the silicate within the range of about 0.50 to3.0 lbs./ gal. and sodium sulfate is added thereto in an amount of from1 to 10% by weight of such silicate solution. In general, it is found tobe advantageous to increase the sodium sulfate content as the sodiumsilicate solution is more dilute. Thus, if a relatively dilute sodiumsilicate solution is prepared, sodium sulfate is supplied in a greateramount, that is to say towards the upper part of the 1 to 10% range.Conversely, more concentrated silicate solutions are combined with alower quantity of sodium sulfate. Where the process is carried out byfeeding separate streams of the thus prepared sodium silicate-sodiumsulfate solution and the aluminum sulfate solution, as is presentlypreferred in the production of tire pigments and newspaper pigmentsespecially suitable concentrations for sodium silicate are found to liewithin the range of about 1.4 to 1.6 lbs./gal., usually about 1.5 lbs./gal. For this particular sodium silicate concentration, the amount ofsodium sulfate supplied is about 5% by weight of the sodium silicatesolution. Such stream is delivered to a reaction chamber containing avolume of fresh Water, such volume being from about 0.4 to about 1.2gallons of water/lb. of silicate, preferably about 0.6 to 1. Where theobjective is to produce pigments especially usable in the shoe industry,in which case preferably the aluminum sulfate is fed directly to thetotal quantity of sodium silicate-sodium sulfate provided as a furtherdiluted reaction medium, the concentration of the prepared sodiumsilicate solution is preferably within the range of about 0.6 to 0.8lbs./gal., usually about 0.70 lbs./ gal. Sodium sulfate in this instanceis employed on the basis of about 3% by weight of the silicate solution.

In the foregoing part of this specification it has been indicated thatthe approach to conducting the precipitation reaction having particularregard to the cornmingling of the total quantities of the reactants issubject to a variety of approaches. More particularly, and somewhat insummary, it has been indicated that a reaction medium may be establishedcontaining from a very small quantity of each of sodium silicate andsodium sulfate up to the total calculated quantity of such materials towhich various reaction media aluminum sulfate is thereafter fed as asubstantially constant stream, the cornmingling taking place withthorough agitation. As will be appreciated, the total quantity of thereactants and the sodium sulfate can be commingled very rapidly or veryslowly and, in any case, the precipitation reaction will proceed. Thus,for example, if the object of bringing the reactants to gether is merelyto produce a sodium alumino silicate in the presence of the minimumquantity of sodium sulfate as herein taught, whereby to obtain a productwithout particular regard to performance characteristics in highlyspecialized applications, or particular applications not requiringnotice of rates of cornmingling of the reactants, it will be appreciatedthat one may disregard consideration of such rates. In general,according to this invention, or otherwise, however, it is not found tobe advantageous to entirely disregard rates of cornmingling because ofthe fact that uniformity of the particulate mass composing the endproducts is rendered poor or economics are adversely affected. Accordingto this invention it is not seen to be desirable in any instance toattempt to complete the reaction in a shorter period of time than about3 minutes regardless of the actual sodium silicate-sodium sulfatereaction medium that has been established, that is to say, the amount ofthe calculated quantity of such materials provided as a dilute medium.Moreover, it may be mentioned that little or no advantage is gained byunduly prolonging the reaction, and therefore, in no instance is itfound to be essential to extend the commingling of the reactants beyonda period of about 75 minutes, such times representing the feed time foraluminum sulfate, and also the sodium silicate-sodium sulfate solutionin those instances where their total quantities are not provided as thereaction medium for receiving the aluminum sulfate. Therefore, as apractical matter commingling of the reactants should take place withinthese extremes, i.e., about 3 to 75 minutes. Usually, however, it is notfound to be especially suitable to approach either extreme too closelyalthough, depending upon the object of the process, that is to say whichproduct is sought having particular high performance characteristics forspecified application such as herein mentioned, it is found that thecornmingling rates are suitably respectively longer or shorter. A moresuitable range for producing pigments of general utility from thestandpoint of particle uniformity in such things as particle size, oilabsorption and surface area is from about 10 to 50 minutes. Moreparticularly, where the total or a major quantity of the calculatedamount of sodium silicate and sodium sulfate is provided as a reactionmedium (such being the preferred approach in producing materials ofhigher usefulness in shoes soles and the like) it is preferred todeliver the aluminum sulfate somewhat more rapidly, for example, withina period not greater than about 25 minutes and preferably within about18 to 20 minutes, sodium silicate and sodium sulfate also being fed tothe reaction within such times where the total of such materials is notalready present in the reaction medium. Further, where the objective isto produce materials better suited for such as the tire and paperindustries, longer cornmingling times are found to be more desirable.Especially in the case of tire pigment production, wherein it ispreferred to provide a reaction medium containing less than 50% of thecalculated total quantity of sodium silicate and sodium sulfate, as forexample 10%, it is found to be preferable that the total of the aluminumsulfate and the remaining quantity of sodium silicate-sodium sulfatesolution be commingled in the reaction medium by delivering separatestreams thereto over a period not less than about 25 minutes, preferably35-40 minutes. Within these indications, it will be appreciated, thatrather precise correlations are necessary with other factors affectingpH of the various reaction media so that the precipitation reactiontakes place according to the more desirable pH conditions indicatedhereinbefore.

Reference has been made heretofore in this specification toconcentrations of sodium silicate and sodium sulfate as well as thedesirable degree of dilution provided by the actual reaction medium. Itwill be appreciated, while bearing in mind that high dilution isdesirable in the production of the type of end product sought(especially overall uniformity of particle character) that dilution ofthe reactants as a practical matter may be accomplished by employingvery highly dilute stream that are delivered to a reaction mediumcontaining a suitable quantity of relatively concentrated sodium sulfatesolution. It also may be remarked that unnecessary dilution merelyintroduces a water removal problem and otherwise affects economics ofthe process. Thus, in specifying hereinafter the concentration ofaluminum sulfate, it will be understood that such is in relation to thetotal quantity of water which may be introduced into the process asgenerally taught and contemplated to be suitable as here inbeforeindicated, other conditions being taken into account. Accordingly,having in mind concentrations which are suitable in relation to theother suitable conditions herein discussed whereby the various productsare obtainable, it has been found that the concentration of the aluminumsulfate stream may vary considerably, however, preferably as a practicalmatter, not less than about 0.1 and not more than about 3.5 lbs/gal.More specifically, and in relation to other conditions indicated to besuitable in connection with products for use in shoe soles and the like,aluminum sulfate concentrations of about 1.2 to about 1.6, specificallyabout 1.4 lbs/gal. are particularly applicable. On the other hand, amore suitable concentration relative to other suitable conditions fortire reinforcing, paper and the like, is from about 2.2 to 2.8lbs./gal., more particularly about 2.5 lbs/gal.

In all instances, the quantity of aluminum sulfate actually fed to theprecipitation reaction is such as to provide a final slurry having a pHlevel consistent with the pH of the desired end product.

No special equipment is required in the processes herein described. Thereaction vessel itself should be equipped with heating means, forexample, a steam jacket, in order to maintain the desired reactiontemperature; also, it should have adequate agitating means to produce astrong backfiow on the body of liquid and thus avoid zones of highconcentration of the incoming reactants. It is desirable to bring thereactants together so as to produce an instantaneous reaction of allmaterial being fed to the fullest extent reasonably possible, as suchpromotes uniformity of the resulting products. Storage vessels equippedwith heating means are provided for the reactants, they being connectedto the reaction vessel thru lines fitted with flow control means. Thereaction vessel is equipped with an outlet line leading to a filterwhich may be of the rotary-string release type, where the precipitate iswater washed to remove sodium sulfate as a liquor, the latter liquorbeing sent to storage. A portion of this sulfate liquor is utilized insucceeding production as the source of the minimum amount of sodiumsulfate needed according to this invention. The filter cake beingthixotropic requires to be liquefied and for this purpose a tank isrequired equipped with a suitable beater. The mass is dried inconventional spray drying equipment.

The immediately following example illustrates detailed procedure andconditions which may suitably be followed in practicing the invention.

EXAMPLE 1 The reaction vessel is charged with gals. of water and asodium silicate (Na O2.5SiO )-sodium sulfate solution of a silicateconcentration of 1.6 lbs/gal. and a sodium sulfate concentration of 5%by weight of the silicate is delivered thereto at a rate of 0.196 g.p.m.(gallons per minute) for one minute. The temperature of the resultingreaction solution is established and maintained at 160 F. Alum inconcentration of 2.6 lbs/gal. at a temperature of 160 F. is delivered tothe reaction volume, the agitator being first started, at a rate of0.066 gal./min. while simultaneously feeding the remaining calculatedquantity of the sodium silicate-sodium sulfate solution at its rate of0.196 g.p.m. This solution being fed over a time of 38 minutes at whichtime it is discontinued. Alum flow is continued until the pH of thereaction mass is lowered to 5.9. A setting or digestion period of min.is observed and pH is again measured and readjusted to the 5.9 value,following which it is delivered to the filter where it is washed withwater for recovery of sodium sulfate and to reduce its residual contentto about 3%. The resulting cake, being solid (thiotropic), is deliveredto a heater and fluidized after which it is spray dryed at an outletpigment temperature of about 220 F. to a moisture content of 5%. Theresulting dry pigment has a pH of 8.5 and the mass is composed ofextremely fine particles relatively few of which are larger than 0.5micron.

Example number... 1 2 3 4 Volume of reaction Water, gallons 10 10 10Silicate feed rate-including Nil'zSOl,

gals/min 0. 196 0. 196 0. 196 0. 196 Initial silicate-sulfate iced-time,mins l 7. 8 19. 5 31. 2 Silicate-sulfate addition time. mins. 38 31. 219. 5 7. 8 Silicate concentration, lbs/gal 1. 6 1. 6 1. 6 1. 6 Saltconcentration in silicate, percent... 5 5 5 5 Alum concentration.lbs/gal 2.6 2. 6 2. 6 2. 6 Concentration silicate in reactor before alumstarts. lbs/gal- 0.03 0.20 0. 44 O. 61 Alum rate. gab/min 0. 066 0.0760.102 0.159 Reaction temperature, F 160 160 160 160 Alum feedtemperature, F 130 130 139 130 Final slurry pI'I.... 5. 9 5. 9 5. 9 5 9Digestion tcmpcraturc. 160 160 160 160 Digestion time 15 15 15 15Pigment pH. 8.5 8. 15 8. 4 8. 0 Rubber results 1100 Initial viscosity.20. 8 23.0 25. 7 29. 5 Minimum viscosit 18. 4 19. 9 22. 4 24. 7 Maximumviscosity. 46. 8 47. 9 49. 9 50. 8 Scorch timc. 2. 64 2. 34 2. 50 3. 168 min. Olsen stiffness. 36. 1 11. O 41. 3 43. 2 8 min. NBS abrasion 7778 70 66 N ewsnrint results:

TA PPI brightness at 5% loading" 6 1. 9 64. 6 64. t 63. 9 TAPPI opacityat 5% loading. 88. 6 87. 8 86. 8 86.5 Ink pick up at 5% loading 2.8 3.03. 7 3. 9 Percent strike thru reduction at 5% loading 73. 8 72. 0 65. 463.6 Percent retention at 5% lo 59. 5 59. 0 57. 3 53. 1

Example number 5 6 7 8 Volume of reaction water, gallons 10 5 1, 800 1,800 Silicate iced rate-including NazSOr,

gals/min 0. 196 0. 250 30. 8 35. 3 Initial silicatc-sulfate feed-time.ruins 39. 0 4 39. 0 4 Silicate-sulfate addition time, niins. 0 35 0 35Silicate concentration, lbs/gal 1. 6 2.0 1. 77 1. 5 Salt concentrationin silicate, percent 5 9. 0 3. 0 7.9 Alum concentration, lbs/gal 2. 0 2.5 1. 4 2. 5 Concentration silicate in reactor before alum starts,lbs/gal 0.69 0.33 0.71 0.11 Alum rate, gaL/min 0.250 0. 119 19. 4 15. 6Reaction tcmpcraturc, F.. 160 140 135 Alum food temperature, F 100 160130 Final slurry pH 5. 9 9.0 5. 9 6.9 Digcstion temperature 160 100 145Digestion timc.- 15 15 15 15 Pigment pH 8. 5 7.3 7. 9 Rubberresultsslioe soles:

Initial viscosity 34. 8 27. O 27. 1 Minimum viscosity... 28. 5 24. 0 24.0 Maximum viscosity-.. 5 1. 6 52. 7 53. 7 Scorch time 3. 41 2. 92 2. 258 min. Olscn stifi'ness 49.9 36. 8 46. 3 8 min. NBS abrasion 60 Nowsorint results:

TAPPI brightness at 5% loading... TAPPI capacity at 5% loading. Ink pickup at 5% loading Percent strike thru reduction at 5% loading Percentretention at 5% lcading.-..

Example number 9 10 Volume of reaction, water, gallons (10% 3 Silicatefeed rate-including NaQSO gal./n1in..... .8 Initial silicate-sulfatefeed-time, mins 4 4 Silicate-sulfate addition time, mins. 35 35 Silicateconcentration, lbs/gal 2.0 2.0 Salt concentration in silicate, percent.7 7 Alum concentration, lbs/gal 2.5 2. 5 Concentration silicate inreactor bcforc alun 0. 24 0. 24 starts, lbs/gal 0. 2A 0. 2i Alum rate,gaL/miu 18 18 Reaction temperature, F 1 10 Alum iced temperature F 149140 Final slurry plI 9.0 6.0 Digestion tempera 140 140 Digestion time...l5 l5 Pigment pH... 10. 2 8. 1 Rubber results 1 Initial viscosity 19.5Minimum viscosity. 16. 3 Maximum viscosity. 43.2 Scorch time 2. 58 8min. Olson stillness. 28. 4 8 min. NBS abrasion 59 Newsprint results:

Example number 11 12 13 14 Volume of reaction water, gallons 255 255Silicate feed rateincluding NazSO4,

gals. lmin 5. 5. 0 6. 41 6. 41 Initial silicate sulfate feed-time,min.... 4 4 39 39 Silicate-sulfate addition time, mins. 35 35 Silicateconcentration, lbs/gal 2. 1. 5 1. 53 1. 53 Salt concentration insilicate- 0. 78 0. 72 0. 23 Alum concentration, lbs/gal 2. 7 2. 7 1.7 1. 0 Concentration silicate in reactor before alum starts,lbs./gal.... 0. 11 1. 53 1. 53 Alum rate, gal/min 1. 39 3.75 2. 50Reaction temperature 150 150 130 Alum feed temperature, F 130 130 150130 Final slurry pH 6.0 6. 0 6.0 6. 9 Digestion temperature 135 150 150130 Digestion time 15 15 15 15 Pigment pH 8. 0 7. 3 9. 6 10.1 Rubberresults tires (oif the roa Tear at 90 min., col 730 660 615 585 Tear at45 min., hot-.. 390 420 340 350 Abrasion at 60 min. cure.... 72. 6 62. 991. 2 96. 4 Flexometer (Firestone), 60 min..... 263 275 267 272 Scorchtime 19. 5 19. 0 17. 5 19. 5 Viscosity 75 78 70 74 Elongation at 90 mincure" 550 550 490 500 Hardness at 90 min. cure 71 70 69 69 Newsprintresults:

TAPPI brightness at 4% loading.-. 64. 6 64. 6 63. 6 63.9 TAPPI opacityat 4% loading 87. 3 87. 4 88.3 87. 9 Ink pickup at 4% loading 4. 8 3. 84. 8 4. 9 Percent strike thru reduction at 4% loa 'ng 65. 0 72. 4 57. 256. 2 Percent retention at 4% loading. 51. 2 50. 0 47. 5 48. 3

Example number 15 16 17 18 Volume of reaction water, gallons 10 10 10Silicate feed rateincluding' NflzSOa,

gals/min 0. 196 0. 196 0. 196 0. 196 Initial silicate-sulfate feed-time,mins- 39 4 39 4 Silicate-sulfate addition time, mins- 0 35 0 35 Silicateconcentration, lbs/gal 0. 71 1. 0 0. 71 1. 5 Silicate mol ratio 3. 3 3.3 2. 0 2. 0 Salt concentration in silicat 6. 0 10.0 3.0 8 Alumconcentration, lbs. lga 1. 4 2. 0 1. 4 2. 5 Concentration silicate inreactor before alum starts, lbs/gal 0. 71 0. 07 0.71 0. 11 Alum rate,gal/min 0.25 0. 057 0. 30 0. 098 Reaction temperature, F... 140 170 140170 Alum feed temperature, F. 140 140 140 130 Final slurry pH 6. 0 7. 06.0 7. 0 Digestion temperature... 140 170 140 170 Digestion time 15 1515 EXAMPLE 19 The reaction vessel is charged with 9 gallons of water anda sodium silicate-sodium sulfate solution of a silicate concentration of2.0 lbs./ gal. and a sodium sulfate concentration of 2% to 6% by weightof the silicate is delivered thereto at a rate of 1162.6 ml./min. Thetemperature of the resulting reaction solution is established andmaintained at 160 F. Alum in concentration of 3.0 lbs/gal. at atemperature of 160 F. is delivered to the reaction medium, the agitatorbeing started first, at a rate of 0.09 to 0.11 g.p.m. (gallons perminute) for 10 seconds or more prior to the start of the sodiumsilicate-sodium sulfate solution at which time the remaining calculatedquantity of the sodium silicate-sodium sulfate solution is started atits rate of 1162.6 mL/min. After 25 minutes, the silicate solution isstopped if the slurry pH is above 8.0. The alum is continued until a pHof 7.8-8.0 is reached. If the pH is below 8.0, the silicate solution iscontinued until a pH of 8.0 is reached. A setting or digestion period of15 minutes is observed and pH is again measured and readjusted to the7.88.0 value, following which it is delivered to the filter where it iswashed with water for recovery of sodium sulfate and to reduce itsresidual content to about 3%. The resulting cake, being solid(thixotropic), is delivered to a beater and fluidized after which it isspray dried at an outlet pigment temperature of about 220 F. to amoisture content of 5%. The resulting dry pigment has a pH of 9.5 andthe mass is composed of extremely fine particles relatively few of whichare larger than 0.5 micron.

Fine paper results:

TAPPI brightness at 9% loading 89.5 TAPPI opacity at 9% loading 87.8

14 The following materials, in the quantities indicated, described astandard testing composition employed to test the exemplary productsherein in rubber for use in tires, more particularly heavy-duty tires ofthe off-the-road type:

Test recipe0ff road tires Parts by wt. 1. Rubber (natural smoked sheets)100.0 2. Carbon black (ISAF-Intermediate super abrasion carbonblack-Huber Corp., Borger, Tex 37.0

3. Pigment (end product or Examples 1-18 herein) 20.0 4. Zinc oxide 5.05. Stearic acid 3.0

6. 6-dodecyl-1,2 dihydro-2,4-trimethyl quinoline ('Santoflex DD) 0.5

7. Polymerized 1,2 dihydro 2,4 trimethyl quinoline ('Flectol H) 1.5 8.Pine tar 5.0 9. Terpene resin acid blend (Turgum S) 2.0 10.Benzothiazole disulfide (MBTS) 0.8 11. Sulfur 2.8

The following materials, in the quantities indicated, de scribed astandard testing composition employed to test the exemplary productsherein in rubber for use in shoe soles, heels, and the like:

Test recipeRubber in shoe Parts by soles and heels: wt./

1. Styrene-butadiene rubber (Pliofiex 1778- SBR, nondiscoloring lowtemperature polymer containing 37 parts light color naphthenic oil per100 parts cold rubber-Mooney viscosity 42-54) 42.8 2. Styrene-butadienerubber (Pliofiex 1510- White, solid low temperature solid coldrubberMooney viscosity of 29-36) 35.0 3. Styrene-butadiene rubber(Pliofiex 1950 White, friable mixture of 50% low temperature SBRcontaining 37 parts of naphthenic oil and 50% high styrene resins) 93.64. Zinc oxide 6.6 5. Zeolex 23 (synthetic pigment material producedaccording to US. Pat. 2,739,073 as by Example 6 herein) 7.0 6. Pigment(products of 'Examples l-5 and 7-18 herein) 70.0 7. Stearic acid 1.0 8.Carbowax ('Polyglycol6000 molecular weight) 4.0 9. Phthalic anhydride.65 10. NOBS Special (N-oxydiethylene benzothiazole-2-sulfenamide) 1.0011. Captax (mercaptobenzothiazole) .80 12. DOTG (diorthotolylquanidine).80 13. Octamine (diphenylamine and diisobutylamine) 1.0 14. Circo LightOil (naphthenic type oil) 15.0 15. Sulfur 2.8

Examples 6 and 9 as presented above are illustrative of the best resultsobtainable following the teachings of US. Pat. No. 2,739,073.

In Examples 1-14 a sodium silicate of the weight ratio l\la 0:2.5SiO wasemployed. 'Examples 15, 16 and 19 indicate procedures and conditionswherein the silicate weight ratio is according to the formula Na0:3.3SiO Examples 17 and 18 illustrate procedures and conditions whereinthe silicate has the ratio of Na O:2.0SiO In Examples 15 to 18 theresults obtainable are entirely s milar to results obtained in the useof the 2.5 ratio silicate carried out according to this invention.

The invention may be practiced utilizing a wide range of silicates, moreparticularly within the range of about 1.5 to 3.5 SiO' :Na O by weight.

The test data, respecting initial, minimum and maximum viscosity andalso scorch time, was derived utilizing the Monsanto Oscillating-DiskRheometer.

What is claimed is:

1. Cured rubber compositions formulated with finely divided precipitatedpigments composed of the oxides of sodium, aluminum and silicon producedby reacting sodium silicate and aluminum sulfate in an aqueous medium,the improvement comprising cured rubber compositions formulated with andcontaining as an improved rubber pigment, finely divided precipitatedsodium alumino silicates consisting essentially of the oxides of sodiumaluminum and silicon, said alumino silicates being produced by reactingsodium silicate and aluminum sulfate in an aqueous medium containingsodium sulfate in an amount equal to at least 1% by weight based on theweight of the silicate and wherein at least about 0.1% of which sulfateis provided in said aqueous medium from the inception of the reaction tothereby form an improved rubber pigment having increased surface areasand oil absorption characteristics.

References Cited UNITED STATES PATENTS ALLAN LIEBERMAN, Primary ExaminerH. H. FLETCHER, Assistant Examiner US. Cl. X.R.

